Recent years, a focus has been placed on a touch detection device capable of detecting an external proximity object which is a so-called a touch panel. The touch panel is mounted on a display device, for example, on a liquid crystal display device, or integrated with the liquid crystal display device, and provided as a display device with a touch detection function.
There is a touch panel capable of using a pen, for example, as the external proximity object. The use of pen makes designation of a small area or input of a handwritten character easier, for example. There are various types of techniques of detecting touch of the pen. One of such various types of techniques is an electromagnetic induction system. This electromagnetic induction system can realize high accuracy and highly accurate detection of writing pressure, and can also realize a function of hovering detection of the external proximity object being spaced apart from a touch panel surface, and thus, the technique is effective as the technique of detecting the touch of the pen.
A touch detection technique that uses the electromagnetic induction system is described in, for example, Japanese Patent Application Laid-Open Publication No. H10 (1998)-49301 (Patent Document 1), No. 2005-352572 (Patent Document 2), and No. 2006-163745 (Patent Document 3).